(1) Field of the Invention
The present invention relates to methods used to fabricate semiconductor devices, and more specifically to a method used to reduce the moisture content in an organic, low dielectric constant, (low k), layer, used to passivate metal interconnect structures.
(2) Description of Prior Art
The use of more conductive metal interconnect structures, comprised of low resistivity metals such as copper, has resulted in decreases in performance degrading RC delays, when compared to counterparts fabricated with more resistive aluminum, or tungsten interconnect structures. In addition the use of low dielectric constant, (low k), materials. have allowed the capacitance value of RC delays to be significantly reduced. Inorganic spin on glass, (SOG), layers, such as silicon oxyfluoride, (SixOFy), or fluorinated silicate glass, (FSG), layers, with dielectric constants as low as 3.4, have been used to replace silicon oxide layers, exhibiting higher dielectric constants, and thus presented higher capacitance values, than FSG layers. Other low k materials, such as an organic layer of poly arylene ether, (PAE), featuring a dielectric constant between about 2.6 to 2.8, is also an attractive low k material, to be used in combination with copper interconnect structures, to result in the desired reductions in RC delay. However when using low k materials such as PAE, or other low k organic materials, the moisture absorbed by the low k organic material, if not reduced, can result in deleterious effects, such as loss of adhesion of the low k material, to overlying, and underlying layers, as well as corrosion of adjacent metal materials, such as copper interconnect structures.
This invention will describe a process for reducing the moisture content in organic low k materials, even if the low k organic material were exposed to the atmosphere for a period of time as great as three months. A high density plasma, (HDP), nitrogen treatment, or other nitrogen type treatments, are used to reduce the moisture in low k materials, without degrading the low k value of this material. The nitrogen treatment can be applied to PAE layers, as well as other organic, low k materials, such as FLARE, (Fluorinated polyARlene Ether polymers), HOSP, (Hydrido Organo Siloxane Polymer), LOSP, (Low Organic Siloxane Polymer). Prior art such as Chen et al, in U.S. Pat No. 5,866,945, as well as Ouellet, in U.S. Pat. No. 5,270,267, describe methods for treating SOG layers, in hydrogen, to restore dangling bonds, and to remove moisture from the SOG layer. However these prior arts do not described the key feature of this present invention in which an organic low k material, such as PAE, is treated in a nitrogen ambient, to reduce the moisture content in the organic low k material, even after the organic low k material had been exposed to the atmosphere for as long as three months.
It is an object of this invention to form a low k layer, overlying, and between, metal interconnect structures.
It is another object of this invention to use an organic material, with a dielectric constant below 2.8, for the low k layer.
It is still another object of this invention to perform a procedure, in a nitrogen ambient, to reduce the moisture content in the organic low k dielectric layer, even when the organic low k layer had been exposed to the atmosphere up to three months.
In accordance with the present invention a method of forming an organic low k layer, located overlying, and between, metal interconnect structures, is described. After formation of metal interconnect structures, overlying, and contacting, conductive regions, such as lower level metal interconnect structures, or active device regions, in a semiconductor structure, an organic layer, such as poly arylene ether, (PAE), with a dielectric constant of less than 2.8, is applied on the underlying metal interconnect structures. A nitrogen treatment, performed in either a high density plasma, (HDP), tool, or in conventional furnaces, is used to reduce the moisture content of the organic low k layer. The nitrogen treatment is effective in reducing the moisture content of organic low k layers, even for the case in which the organic low k layer had been exposed to the environment for a time period of up to three months.